1. Field of the Invention
The present invention relates to a control apparatus for a vehicular automatic transmission configured to change a speed of a rotary motion received by an input shaft thereof and to output the rotary motion of the changed speed from an output shaft thereof.
2. Discussion of Related Art
There is known a control apparatus for an automatic transmission of a vehicle which includes hydraulically operated coupling elements and planetary gear sets and which performs shifting actions by engaging and releasing actions of the coupling elements. JP-6-341536A discloses an example of a control apparatus for such a vehicular automatic transmission. This control apparatus is configured to control a so-called “clutch-to-clutch shifting action” wherein a releasing-side coupling element which has been placed in an engaged state prior to the shifting action is released, while at the same time an engaging-side coupling element which has been placed in a released state prior to the shifting action is engaged.
It has been desired to shorten the time required to perform a shifting action of the vehicular automatic transmission, while reducing a shifting shock upon the shifting action, for improving drivability and driving comfort of the vehicle. For shortening the required shifting time, it is required to increase a rate of change of the rotating speed of an input shaft of the automatic transmission during the shifting action. To increase the rate of change of the rotating speed of the input shaft during the shifting action controlled by the control apparatus disclosed in the above-identified publication JP-6-341536A, it is required to increase a rate of increase of an engaging force of the engaging-side coupling element. However, an increase of the rate of increase of the engaging force undesirably results in an increase of the shifting shock. Thus, the control apparatus of the above-identified publication suffers from difficulty in shortening the required shifting time without an increase of the shifting shock.